Carbon sequestration, or the capture of carbon dioxide gases resultant from an industrial process, has long been known, whereby the gas reacts with available calcium and magnesium oxides to form minerals that are relatively stable, such as in the reaction below1:CaO+CO2→CaCO3(calcite)MgO+CO2→MgCO3(magnesite)
There is an abundance of peridotite ophiolite rocks in certain regions of the world, which are mafic rocks that contain high amounts of such Ca and Mg metal oxides, on and near the surface of the Earth. The surface mineralogy has been known to change when in contact with pollutants such as large amounts of CO2 from oil and gas refineries.
There are numerous propositions to inject CO2 into subterranean saline bedrock (brines), abandoned oil wells, and igneous rock formations in situ, however, the present inventors contend that, short of sending the CO2 deep into the Earth's mantle, about 5 miles (8 km) below the oceanic crust and 20 miles (32 km) below the continental crust, no one can guarantee against leakage due to the very act of injection fracturing of rock with intention to store, allowing for unforeseeable conduits back to the surface. Also, due to natural causes such as infiltration by groundwater (evident in many regions by the dissolution of bedrock carbonates and precipitation as stalagtites and stalagmites in caves), shifting of bedrock by earthquake or human induced “secondary drilling intrusion” (deliberate or unintended release of buried materials/gases by further drilling into bedrock originally intended for perpetual storage), or simple escape of the CO2 by upward permeation trough cracks or porous rock under high pressure due simply to the depth at which such rocks exist. The costs of injection can be expected to be high if there is no return by further oil and gas recovery, and higher electric bills for power sources involved in the recovery would be absorbed by the customer.
It is contended that artificial heating and pressurization would not be enough to speed the reaction of CO2 with peridotite in-situ. However, although there is research under way by various institutions, there is no conclusive experimental evidence that the speed of the reaction cannot be enhanced. There is also no guarantee that the reaction of conversion of CO2 to carbonates would go to completion as required at great depths below the Earth's surface, nor that thereafter, the rocks would be undisturbed by natural or human induced events. Detailed plans exist for the burial of nuclear wastes, but for the same reasons mentioned above, no responsible nation/organization has yet attempted such burial.
Of the billions of tons of CO2 necessary to be sequestered for any significant impact on emissions reduction (25 billion metric tons emitted worldwide in 2003)2, it is claimed by Kelemen et al3, that peridotite fields are naturally absorbing between 10,000 and 100,000 tons of CO2 per year. The researchers calculate that 2 tons of CO2 can be absorbed per cubic kilometer (2 tons/km3) of peridotite, and say that this can be enhanced by a factor of 100,000. In order to avoid the costs of mining and transporting the peridotite to industrial centers, they explain that in situ injection of CO2 could enhance the process, to absorb about 4 billion tons of CO2 annually, roughly 13 percent of the total sent into the atmosphere3.